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          Kotlin 集合使用
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        <h2 id="Collection"><a href="#Collection" class="headerlink" title="Collection"></a>Collection</h2><pre><code>学习一门新语言, 大致看一下与已的语言的差异, 然后根据需求来学习, 涉及到的陌生语法, 即时查找, 然后复盘总结所需的语法知识.

学习kotlin太轻敌了, 拖了那么长时间, 竟然不知道该如何学习</code></pre><h2 id="需求"><a href="#需求" class="headerlink" title="需求"></a>需求</h2><ol start="0">
<li><p>学习MaterialDialog的使用</p>
<ul>
<li>看源码学习才是最高效的</li>
</ul>
</li>
<li><p>array 的使用</p>
</li>
<li><p>List的使用</p>
</li>
<li><p>Map的使用</p>
</li>
<li><p>Stack 的使用</p>
</li>
<li><p>Heap 的使用</p>
</li>
<li><p>实现排序算法</p>
</li>
</ol>
<h2 id="陌生语法"><a href="#陌生语法" class="headerlink" title="陌生语法"></a>陌生语法</h2><ol>
<li><p>init</p>
<ul>
<li>inline class 不能有init{}块</li>
<li>相当于java中的静态初始化块</li>
</ul>
</li>
<li><p>setter, getter</p>
<ul>
<li>kotlin会为属性自动生成 setter/getter, 前提是可以自动推断出默认初始化器(定义时赋值), val 定义的属性在声明时未赋值, 后面只能在Constructor中赋值</li>
<li>访问属性是通过setter/getter, 所以, 在setter中直接访问属性名赋值会形成无限递归调用,引发StackOverflow</li>
<li>避免此问题, kotlin的实现是在getter/setter 中自动添加一个backing field - field, field 只存在getter/setter中</li>
<li>扩展的属性需要手动实现getter/setter, 因为, kotlin对于扩展属性没有一个好的方法去添加backing field</li>
<li>那么原有属性是如何将field关联的呢?</li>
</ul>
</li>
<li><p>Backing Fields</p>
<ul>
<li>只存在于accessors 中</li>
<li>如果backing field 不能实现需求, 可以使用私有变量来实现, 编译器会将其优化为直接访问属性</li>
</ul>
</li>
<li><p>var, val</p>
<ul>
<li>var 声明可变属性/变量, val 声明只读属性/变量</li>
<li>变量的作用域与其第一次声明的位置有关</li>
<li><a href="http://www.liying-cn.net/kotlin/docs/reference/properties.html" target="_blank" rel="noopener">properties文档</a></li>
</ul>
</li>
<li><p>编译期常数值</p>
<ul>
<li>const 修饰, </li>
<li>必须是顶级属性, 或 object , companion object 修饰</li>
<li>值被初始化为String类型, 或基本类型</li>
<li>不存在自定义取值方法 </li>
</ul>
</li>
<li><p>对象表达式object, companion object</p>
<ul>
<li>可以声明一个匿名对象, 如果object 没有超类, 则是Any, 不能访问匿名对象中的属性</li>
<li>使用object实现的匿名对象不需要像java 添加final 修饰</li>
<li>companion object 的访问形式类似于静态成员, 但是companion object是一个对象, 可以实现接口, 加上@JvmStatic 可以真正实现静态成员</li>
<li>将一个类名直接赋值给变量, 默认赋值访问的是companion object</li>
</ul>
</li>
</ol>

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